xii 
CONTENTS. 
PAGE 
Sect. 23. Torsion ............. 859 
„ 24. The Twining of Climbing -Plants 862 
„ 25. The Twining of Tendrils 865 
„ 26. Movements of growing Leaves and Floral Organs produced by Variations 
of Light and of Temperature 871 - 
CHAPTER V. 
Periodic Movements of the Mature Parts of Plants and Movements 
dependent on Irritation. 
Sect, 27. Introduction . 878 
„ 28. Review of the Phenomena connected with Periodically Motile and Irritable 
Parts of Plants 880 
„ 29. Mechanism of the Movements caused by Contact or Concussion . . 887 
30. Mechanism of the Moyements produced by Variations of Temperature 
and of Light 894 
„ 31. Mechanism of spontaneous periodic Movements ...... 895 
CHAPTER VL 
The Phenomena of Sexual Reproduction. 
Sect. 32. The Nature of Sexuality 896 
„ 33. Influence of the origin of the Reproductive Cells on the product of 
Fertilisation 904 
„ 34. Hybridisation ............ 914 
CHAPTER VH. 
The Origin of Species. 
Sect. 35. Origin of Varieties 920 
„ 36. Accumulation of new characters in the Reproduction of Varieties . . 924 
„ 37. Causes of the Progressive Development of Varieties 928 
„ 38. Relationship of the Morphological Nature of the Organ to its adaptation to 
the Conditions of Plant-life 933 
„ 39. The Theory of Descent 940 
Appendix 945 
Index , 963 
